Negative photosensitive composition and negative photosensitive lithographic printing plate

ABSTRACT

There are provided a negative-working photosensitive composition which can be cured by infrared rays and is less likely to suffer polymerization inhibition by oxygen during radical polymerization, and also exhibits high adhesion with a metal, and a negative-working photosensitive lithographic printing plate which is capable of directly forming images by irradiation with infrared rays from a solid or semiconductor laser based on digital signals, and also has high sensitivity and excellent printing durability. The negative-working photosensitive composition contains an infrared absorber (A), an organoboron compound (B) which functions as a polymerization initiator by using in combination with the infrared absorber (A), a compound having a polymerizable unsaturated group (C) and a diazo resin (D), and the negative-working photosensitive lithographic printing plate comprises a support, and a photosensitive layer containing the negative-working photosensitive composition formed on the support.

TECHNICAL FIELD

The present invention relates to a negative-working photosensitivecomposition and a negative-working photosensitive lithographic printingplate used in the offset printing field and, more particularly, to anegative-working photosensitive lithographic printing plate used as aso-called computer-to-plate (CTP) plate capable of directly formingimages, by irradiation with infrared rays from a solid or semiconductorlaser based on digital signals, and a negative-working photosensitivecomposition suitable for use in a photosensitive layer of such alithographic printing plate.

PRIOR ART

With the progress of computer image processing techniques, a method ofdirectly writing images by light irradiation corresponding to digitalsignals has recently been developed. An intense interest has been showntowards a computer-to-plate (CTP) system of directly forming images on aphotosensitive lithographic printing plate, without outputting theimages to silver salt mask films by utilizing this method inlithographic printing plates. A CTP system using a high-output laser,having a maximum intensity within a near infrared or infrared range as asource of light, has advantages such that high-resolution images can beobtained by exposure in a short time and a photosensitive lithographicprinting plate used in the system can be handled in daylight.Particularly, high-output and small-sized lasers are easily available assolid and semiconductor lasers, which emit infrared rays having awavelength within a range from 760 to 1200 nm.

As the negative-working photosensitive lithographic printing plate whichcan form images using the solid or semiconductor laser, anegative-working photosensitive lithographic printing plate comprising aphotosensitive layer comprising of a negative-working photosensitivecomposition containing an alkali-soluble resin (novolak resin, etc.), acompound capable of being crosslinked by an acid (acid crosslinkingagent such as a resol resin), a compound capable of generating an acidby heat (acid generator), and a photothermal converting agent (infraredabsorber such as a dye or pigment) has been proposed in JapaneseUnexamined Patent Publication (Kokai) No. 7-20629 (Patent Document 1).

In this negative-working photosensitive lithographic printing plate, itis found that negative images are formed in the following manner. First,when the photosensitive layer is irradiated with infrared rays from thesolid or semiconductor laser, infrared rays are converted into heat bythe photothermal converting agent in the photosensitive layer. An acidis generated, from the acid generator, by the heat. When pre-heatedprior to development, a catalytic action of the acid causes thecrosslinking reaction between the acid crosslinking agent and thealkali-soluble resin or the crosslinking reaction between the acidcrosslinking agents, and thus the photosensitive layer exposed toinfrared rays is made insoluble in an alkali developing solution.Consequently, an image area is formed.

However, this negative-working photosensitive lithographic printingplate must be pre-heated prior to development and, therefore, anegative-working photosensitive lithographic printing plate, which doesnot require pre-heating, has been desired.

As the negative-working photosensitive lithographic printing plate whichcan form images using the solid or semiconductor laser and does notrequire pre-heating, a negative-working photosensitive lithographicprinting plate having a photosensitive layer comprising of anegative-working photosensitive composition containing an infraredabsorber, an onium salt, a radical polymerizable compound and a binderis proposed in Japanese Unexamined Patent Publication (Kokai) No.2001-125260 (Patent Document 2).

In this negative-working photosensitive lithographic printing plate, theonium salt functions as an initiator of radical polymerization.Therefore, when irradiated with infrared rays, radical polymerization ofthe radical polymerizable compound proceeds and the photosensitive lateris cured and, thus, the photosensitive layer exposed to infrared rays ismade insoluble in a developing solution. Consequently, an image area isformed.

However, this negative-working photosensitive lithographic printingplate had a problem in that it has low sensitivity because thepolymerization is inhibited by oxygen in an air during the radicalpolymerization, and is also inferior in printing durability because theimage area thus formed has insufficient strength. In thenegative-working photosensitive lithographic printing plate,deterioration of printing durability was caused by poor adhesion withmetal as a support of the photosensitive layer.

(Patent Document 1)

Japanese Unexamined Patent Publication (Kokai) No. 7-20629

(Patent Document 2)

Japanese Unexamined Patent Publication (Kokai) No. 2001-125260

DISCLOSURE OF THE INVENTION

Thus, an object of the present invention is to provide anegative-working photosensitive composition which can be cured byinfrared rays and is less likely to suffer polymerization inhibition, byoxygen, during radical polymerization, and also exhibits high adhesionwith metal, and a negative-working photosensitive lithographic printingplate which is capable of directly forming images by irradiating withinfrared rays from a solid or semiconductor laser based on digitalsignals, and also has high sensitivity and excellent printingdurability.

That is, a negative-working photosensitive composition comprising:

(A) an infrared absorber,

(B) an organoboron compound which functions as a polymerizationinitiator by using in combination with the infrared absorber (A),

(C) a compound having a polymerizable unsaturated group, and

(D) a diazo resin.

The infrared absorber (A) is preferably a near infrared absorbablecationic dye represented by the following formula (1):D⁺A⁻  (1)wherein D⁺ represents a cationic dye having an absorption within a nearinfrared range, and A⁻ represents an anion.

The organoboron compound (B) is preferably an ammonium salt of aquaternary boron anion represented by the following formula (2):

wherein R¹, R², R³ and R⁴ each independently represents an alkyl group,an aryl group, an alkaryl group, an allyl group, an aralkyl group, analkenyl group, an alkynyl group, an alicyclic group, or a saturated orunsaturated heterocyclic group, and at least one of R¹, R², R³ and R⁴ isan alkyl group having 1 to 8 carbon atoms, and R⁵, R⁶, R⁷ and R⁸ eachindependently represents a hydrogen atom, an alkyl group, an aryl group,an allyl group, an alkaryl group, an aralkyl group, an alkenyl group, analkynyl group, an alicyclic group, or a saturated or unsaturatedheterocyclic group.

The negative-working photosensitive composition of the present inventionfurther comprises a binder resin (E), preferably.

The binder resin (E) is preferably an alkali-soluble resin.

The negative-working photosensitive lithographic printing plate of thepresent invention comprises a support, and a photosensitive layercontaining the negative-working photosensitive composition of thepresent invention formed on the support.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.

<(A) Infrared Absorber>

The infrared absorber (A) in the present invention is a substancewherein a maximum absorption wavelength is within a near infrared orinfrared range and, for example, is a substance wherein a maximumabsorption wavelength is within a range from 760 nm to 1200 nm. Examplesof the substance include various pigments or dyes.

The pigments used in the present invention are commercially availablepigments, and are described, for example, in Color Index, “LatestPigment Handbook”, (edited by the Japan Association of PigmentTechnology, 1977 edition), “Latest Pigment Application Technologies”(CMC, 1986), and “Printing Ink Technologies” (CMC, 1984). Examples ofthe pigments include black pigments, yellow pigments, orange pigments,brown pigments, red pigments, purple pigments, blue pigments, greenpigments, fluorescent pigments, and polymers containing chemicallycombined dyes. Specific examples of the pigments are insoluble azopigments, azo lake pigments, condensed azo pigments, chelated azopigments, phthalocyanine-based pigments, anthraquinone-based pigments,perylene- and perinone-based pigments, thioindigo-based pigments,quinacridone-based pigments, dioxazine-based pigments,isoindolinone-based pigments, quinophthalone-based pigments, dyed lakepigments, azine pigments, nitroso pigments, nitro pigments, naturalpigments, fluorescent pigments, inorganic pigments, and carbon black.

Among these pigments, carbon black is preferably used as a substancewhich efficiently absorbs light within a near infrared or infrared rangeand is economically excellent. As these carbon blacks, grafted carbonblacks, which have various functional groups and are excellent indispersibility, are commercially available and are described on page 167of “Carbon Black Handbook, Third Edition” (edited by the Association ofCarbon Black, 1995) and page 111 of “Characteristics and OptimumFormulation of Carbon Black and Application Technique” (edited by theAssociation of Technical Information, 1997), and any of these carbonblacks can be preferably used in the present invention.

These pigments may be used without being surface-treated or may be usedafter being subjected to surface treatments known in the art. The knownsurface treatments include a treatment wherein a resin or a wax iscoated on the surface of the pigments, a treatment wherein a surfaceactive agent is adhered to the surface of the pigments, and a treatmentwherein a reactive substance such as a silane coupling agent, an epoxycompound or a polyisocyanate is bonded to the surface of the pigments.These surface-treating methods are described in “Properties andApplications of Metal Soaps” (Saiwai Shobo K. K.), “Latest PigmentApplication Technologies” (CMC, published 1986), and “Printing InkTechnologies” (CMC, published 1984).

The particle diameter of the pigments used in the present invention ispreferably within a range from 0.01 to 15 μm, and more preferably from0.01 to 5 μm.

The dyes used in the present invention are commercially available dyesand dyes known in the art and described, for example, in “Dye Handbook”(edited by the Association of Organic Synthesis Chemistry, published1970), “Handbook of Color Material Engineering” (edited by the JapanSociety of Color Material, Asakura Shoten K. K., published 1989),“Technologies and Markets of Industrial Pigments” (CMC, published 1983),and “Chemical Handbook, Applied Chemistry Edition” (edited by TheChemical Society of Japan, Maruzen Shoten K. K., published 1986).Specific examples of the dyes include azo dyes, azo dyes in the form ofmetal complex salts, pyrazolone azo dyes, anthraquinone dyes,phthalocyanine dyes, carbonium dyes, quinonimine dyes, methine dyes,cyanine dyes, indigo dyes, quinoline dyes, nitro-based dyes, xanthenedyes, thiazine-based dyes, azine dyes, and oxazine dyes.

The dyes which absorb light within a near infrared or infrared rangeare, for example, cyanine dyes, methine dyes, naphthoquinone dyes,squalirium dyes, arylbenzo(thio)pyridinium salts, trimethinethiapyryliumsalts, pyrylium compounds, pentamethinethiapyrylium salts, and infraredabsorbing dyes.

Among these dyes, the infrared absorber (A) is preferably a nearinfrared absorbable cationic dye represented by the following formula(1):D⁺A⁻  (1)wherein D⁺ represents a cationic dye having an absorption within a nearinfrared range, and A⁻ represents an anion, because it efficientlyenables an organoboron compound (B) described hereinafter to exert apolymerization function.

Examples of the cationic dye having an absorption within a near infraredrange include cyanine-based dyes, triarylmethane-based dyes,aminium-based dyes, and diimmonium-based dyes, which have an absorptionwithin a near infrared range. Specific examples of the cationic dyehaving an absorption within a near infrared range include the following.

Examples of the anion include the halogen anions ClO₄ ⁻, PF₆ ⁻, BF₄ ⁻,SbF₆ ⁻, CH₃SO₃ ⁻, CF₃SO₃ ⁻, C₆H₅SO₃ ⁻, CH₃C₆H₄SO₃ ⁻, HOC₆H₄SO₃ ⁻,ClC₆H₄SO₃ ⁻, and a boron anion represented by the following formula (3).The boron anion is preferably a triphenyl n-butylboron anion or atrinaphthyl n-butylboron anion.

wherein R¹, R², R³ and R⁴ each independently represents an alkyl group,an aryl group, an alkaryl group, an allyl group, an aralkyl group, analkenyl group, an alkynyl group, an alicyclic group, or a saturated orunsaturated heterocyclic group, and at least one of R¹, R², R³ and R⁴ isan alkyl group having 1 to 8 carbon atoms.

As the cationic dye having an absorption within a near infrared range,those represented by the following formula (4) are preferable. As thesedyes have a maximum absorption wavelength within a range from 817 to 822nm, the resulting photosensitive lithographic printing plate is suitablefor an exposing machine equipped with an existing near infraredsemiconductor laser. As a molar extinction coefficient is 1×10⁵ or more,the resulting photosensitive lithographic printing plate is excellent insensitivity.

wherein X represents N(C₂H₅)₂ or N(CH₃)₂, Y represents N(C₂H₅)₂, H orOCH₃, and Z⁻ represents any of anions represented by the followingformulas.

The infrared absorber (A) is used by adding it to a negative-workingphotosensitive composition after selecting at least one suitable pigmentor dye capable of absorbing a specific wavelength of a light sourcedescribed hereinafter from among the pigments or dyes described above.

When the pigment is used as the infrared absorber (A), the content ofthe pigment is preferably within a range from 0.5 to 15% by weight, andparticularly preferably from 1 to 10% by weight, based on the totalsolid content of the negative-working photosensitive composition. Whenthe content of the pigment is less than 0.5% by weight, infrared raysare not sufficiently absorbed. On the other hand, when the content ofthe pigment is more than 15% by weight, an excess amount of heat tendsto be generated. Therefore, it is not preferred.

When the dye is used as the infrared absorber (A), the content of thedye is preferably from 0.5 to 15% by weight, and particularly preferablyfrom 1 to 10% by weight, based on the total solid content of thenegative-working photosensitive composition. When the content of thepigment is less than 0.5% by weight, infrared rays are not sufficientlyabsorbed. On the other hand, when the content of the dye is more than15% by weight, absorption of infrared rays is substantially saturatedand thus the addition effect may not be enhanced. Therefore, it is notpreferred.

<(B) Organoboron Compound>

The organoboron compound (B) used in the present invention functions asa polymerization initiator by using in combination of the infraredabsorber (A) described above. The organoboron compound (B) is preferablyan ammonium salt of a quaternary boron anion represented by thefollowing formula (2):

wherein R¹, R², R³ and R⁴ each independently represents an alkyl group,an aryl group, an alkaryl group, an allyl group, an aralkyl group, analkenyl group, an alkynyl group, an alicyclic group, or a saturated orunsaturated heterocyclic group, and at least one of R¹, R², R³ and R⁴ isan alkyl group having 1 to 8 carbon atoms, and R⁵, R⁶, R⁷ and R⁸ eachindependently represents a hydrogen atom, an alkyl group, an aryl group,an allyl group, an alkaryl group, an aralkyl group, an alkenyl group, analkynyl group, an alicyclic group, or a saturated or unsaturatedheterocyclic group.

Among these organoboron compounds, there can be preferably used tetran-butylammonium triphenylboron, tetra n-butylammonium trinaphthylboron,tetra n-butylammonium tri(p-t-butylphenyl)boron, tetramethylammoniumn-butyltriphenylboron, tetramethylammonium n-butyltrinaphthylboron,tetramethylammonium n-octyltriphenylboron, tetramethylammoniumn-octyltrinaphthylboron, tetraethylammonium n-butyltriphenylboron,tetraethylammonium n-butyltrinaphthylboron, trimethylhydrogenammoniumn-butyltriphenylboron, triethylhydrogenammonium n-butyltriphenylboron,tetrahydrogenammonium n-butyltriphenylboron, tetramethylammonium tetran-butylboron, and tetraethylammonium tetra n-butylboron.

The organoboron compound (B) in the present invention can function as apolymerization initiator by irradiation with infrared rays to generate aradical (R.), as shown in the following scheme (5):

wherein Ph represents a phenyl group, R represents an alkyl group having1 to 8 carbon atoms, and X⁺ represents an ammonium ion, when using incombination with the infrared absorber (A) (for example, D⁺A⁻).

The content of the organoboron compound (B) is preferably within a rangefrom 1 to 15% by weight, and particularly from 3 to 10% by weight, basedon the solid content of the negative-working photosensitive composition.When the content of the organoboron compound (B) is less than 1% byweight, insufficient polymerization reaction causes insufficient curing,resulting in weak image area of the photosensitive lithographic printingplate. On the other hand, when the content of the organoboron compound(B) is more than 15% by weight, the polymerization reaction does notproceed efficiently. If necessary, two or more organoboron compounds (B)may be used. Also the organoboron compound (B) may be used incombination with known polymerization initiators used in the radicalpolymerization, such as triazines.

<(C) Compound having a Polymerizable Unsaturated Group>

The compound having a polymerizable unsaturated group (C) in the presentinvention is a monomer or oligomer having one, and preferably two ormore, addition-polymerizable ethylenically unsaturated groups, and theboiling point at normal pressure is preferably 100° C. or higher.

Examples of the monomer or oligomer include monofunctional(meth)acrylates such as polyethylene glycol mono(meth)acrylate[hereinafter, methacrylate and acrylate are referred generically as(meth)acrylate], polypropylene glycol mono(meth)acrylate, andphenoxyethyl (meth)acrylate; polyfunctional (meth)acrylates such aspolyethylene glycol di(meth)acrylate, polypropylene glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, neopentyl glycoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, hexanedioldi(meth)acrylate, tri(acryloyloxyethyl) isocyanurate, (meth)acrylate ofpolyhydric alcohol-alxylene oxide adduct, (meth)acrylate of polyhydricphenol.alkylene oxide adduct, urethane acrylates, polyester acrylates,epoxy acrylates obtained by adding epoxy resin and (meth)acrylic acid;and polyfunctional allyl compounds such as allyl isocyanurate and allylcyanurate.

The content of the compound having a polymerizable unsaturated group (C)is preferably within a range from 5 to 60% by weight based on the solidcontent of the negative-working photosensitive composition. When thecontent of the compound having a polymerizable unsaturated group (C) isless than 5% by weight, sufficient curing is not attained. On the otherhand, when the content of the compound having a polymerizableunsaturated group (C) is more than 60% by weight, the resultingphotosensitive lithographic printing plate has a sticky photosensitivelayer. If necessary, two or more compounds having a polymerizableunsaturated group (C) may be used in combination.

<(D) Diazo Resin>

Examples of the diazo resin (D) include diazo resins typified by a saltof a condensate of diazodiarylamine and an active carbonyl compound.

Examples of particularly preferable diazo resin include organic orinorganic acid salts of condensates of 4-diazodiphenylamine,4-diazo-3-methyldiphenylamine, 4-diazo-4′-methyldiphenylamine,4-diazo-3′-methyldiphenylamine, 4-diazo-4′-methoxydiphenylamine,4-diazo-3-methyl-4′-ethoxydiphenylamine, and4-diazo-3-methoxydiphenylamine with formaldehyde, paraformaldehyde,acetaldehyde, benzaldehyde, and 4,4′-bis-methoxymethyl diphenyl ether.

Examples of the organic acid of the diazo resin include methanesulfonicacid, benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid,mesitylenesulfonic acid, dodecylbenzenesulfonic acid,naphthalenesulfonic acid, propylnaphthalenesulfonic acid,1-naphthol-5-sulfonic acid, 2-nitrobenzenesulfonic acid,3-chlorobenzenesulfonic acid, and2-hydroxy-4-methoxybenzophenone-5-sulfonic acid. Examples of theinorganic acid include hexafluorophosphoric acid, tetrafluoroboric acidand thiocyanic acid.

There can also be used a diazo resin wherein a main chain is a polyestergroup; a diazo resin obtained by reacting a polymer having a carboxylicanhydride residue with a diazo compound having a hydroxyl group; and adiazo resin obtained by reacting a polyisocyanate compound with a diazocompound having a hydroxyl group.

The content of the diazo resin (D) is preferably within a range from 1to 15% by weight based on the solid content of the composition. When thecontent of the diazo resin (D) is less than 1% by weight, a sufficientadhesion with metal is not attained. On the other hand, when the contentof the diazo resin (D) is more than 15% by weight, the unreacted iazoresin may remain and the non-image area of the photosensitivelithographic printing plate may be contaminated with ink. If necessary,two or more diazo resins (D) may be used in combination.

<(E) Binder Resin>

As the binder resin (E) in the present invention, there can be used abinder resin which has conventionally been used in a negative-workingphotosensitive lithographic printing plate. As the binder resin, forexample, there can be used copolymers such as (meth)acrylicacid-(meth)acrylate copolymer, copolymer containing hydroxyalkyl(meth)acrylate and (meth)acrylonitrile, copolymer having an aromatichydroxyl group, and a polymer having a 2-hydroxy-3-phenoxypropyl(meth)acrylate unit; epoxy resins; polyamide resins; vinyl halides suchas polyvinyl chloride and polyvinylidene chloride; vinyl polyacetates;polyesters; acetal resins such as formal resin and butyral resin;soluble polyurethane resins which are commercially available fromGoodrich Corporation, USA under the trade name of Estan; polystyrenes;styrene-maleic anhydride copolymers or half esters thereof; cellulosederivatives; shellacs; rosin or modified compounds thereof; andcopolymers having an unsaturated group in the side chain.

The binder resin (E) is preferably an alkali-soluble resin because itbecomes possible to develop it with a developing solution such as analkali aqueous solution.

The alkali-soluble resin refers to a binder resin which is insoluble inwater and is soluble in an alkali aqueous solution, and specificexamples thereof include resins having an alkali-soluble group such ascarboxyl group, phenolic hydroxyl group, sulfonic acid group, phosphonegroup, active imino group, or N-sulfonyl amide group.

Examples of the alkali-soluble resin include novolak or resol resinssuch as phenol-formaldehyde resin, cresol-formaldehyde resin, andphenol-cresol-formaldehyde cocondensed resin; polyhydroxystyrenes suchas polyhydroxystyrene and polyhalogenanted hydroxystyrene; acrylicresins having one or more units derived from a monomer having an acidicgroup, such as N-(4-hydroxyphenyl)methacrylamide, hydroquinonemonomethacrylate, N-(sulfamoylphenyl)methacrylamide, N-phenylsulfonylmethacrylamide, N-phenylsulfonyl maleimide, acrylic acid, andmethacrylic acid; vinyl-based resins having an active methylene groupand a urea bond; polyurethane resins such as polyurethane resin havingan N-sulfonyl amide group, an N-sulfonyl ureide group or anN-aminosulfonyl amide group, and polyurethane resin having an activeimino group, and polyurethane resin having a carboxyl group; polyamideresins such as polyhydroxypolyamide; and polyester resins having aphenolic hydroxyl group.

As the binder resin (E), a binder resin having a polymerizableunsaturated group such as acryloyl group, methacryloyl group or allylgroup in the side chain is preferably used. As such a binder resincauses a crosslinking reaction with the compound having a polymerizableunsaturated group (C) and the crosslink density increases, the resultingphotosensitive lithographic printing plate has more improved printingdurability.

The content of the binder resin (E) is preferably within a range from 20to 70% by weight based on the solid content of the negative-workingphotosensitive composition. When the content of the binder resin (E) isless than 20% by weight, sufficient curing is not attained, resulting inweak image area of the photosensitive lithographic printing plate. Onthe other hand, when the content of the binder resin (E) is more than70% by weight, the curing reaction does not proceed efficiently. Ifnecessary, two or more binder resins (E) may be used in combination.

<Negative-Working Photosensitive Composition>

To the negative-working photosensitive composition of the presentinvention, additives known in the art, such as colorants (dyes,pigments), surfactants, plasticizers, stability modifies andpolymerization inhibitors can be added, if necessary.

Examples of preferable dye include basic oil-soluble dyes such asCrystal Violet, Malachite Green, Victoria Blue, Methylene Blue, EthylViolet, and Rhodamine B. Examples of the commercially available productsthereof include “Victoria Pure Blue BOH” (manufactured by HODOGAYACHEMICAL Co., Ltd.), “Oil Blue #603” (manufactured by Orient ChemicalIndustries, Ltd.), “VPB-Naps (naphthalenesulfonate of Victoria PureBlue)” [manufactured by HODOGAYA CHEMICAL Co., Ltd.], and “D11”[manufactured by PCAS Co.]. Examples of the pigment includePhthalocyanine Blue, Phthalocyanine Green, Dioxadine Violet, andQuinacridone Red.

Examples of the surfactant include fluorine-based surfactants andsilicone-based surfactants.

Examples of the plasticizer include diethyl phthalate, dibutylphthalate, dioctyl phthalate, tributyl phosphate, trioctyl phosphate,tricresyl phosphoate, tri(2-chloroethyl)phosphate, and tributyl citrate.

As the stability modifier known in the art, for example, phosphoricacid, phosphorous cid, oxalic acid, tartaric acid, malic acid, citricacid, dipicolinic acid, polyacrylic acid, benzenesulfonic acid, andtoluenesulfonic acid can also be used in combination.

Examples of the polymerization inhibitor include known phenoliccompounds, quinones, N-oxide compounds, amine-based compounds, sulfidegroup-containing compounds, nitro group-containing compounds, andtransition metal compounds. Specific examples thereof includehydroquinone, p-methoxyphenol, p-cresol, pyrogallol, t-butylcatechol,benzoquinone, 4,4′-thiobis(3-methyl-6-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol), 2-mercaptobenzimidazole,and N-nitrosophenylhydroxyamine primary cerium salt.

The amount of these additives to be added varies depending on thepurpose, but is preferably within a range from 0 to 30% by weight basedon the solid content of the photosensitive composition.

In the negative-working photosensitive composition described above, asthe infrared absorber (A) is used in combination with the organoboroncompound (B) which functions as a polymerization initiator by using incombination with the infrared absorber (A), the polymerization of thecompound having a polymerizable unsaturated group (C) proceeds due toinfrared rays. Also the decomposition and crosslinking of the diazoresin (D) proceed when the infrared absorber (A) absorbs infrared rays.Therefore, this negative-working photosensitive composition can be curedby infrared rays.

Although the reason is not elucidated, by using the organoboron compound(B) as the polymerization initiator, polymerization inhibition is lesslikely to be caused by oxygen during the radical polymerization. Alsocuring proceeds by the decomposition and crosslinking of the diazo resin(D), which is not influenced by oxygen. Therefore an influence of oxygenon polymerization inhibition is reduced. Adhesion with the support madeof metal is remarkably improved by the diazo resin (D).

As described above, by using the negative-working photosensitivecomposition, which is less likely to cause polymerization inhibition byoxygen during radical polymerization and also exhibit high adhesion withmetal, as a photosensitive layer of a negative-working photosensitivelithographic printing plate, it becomes possible to obtain anegative-working photosensitive lithographic printing plate which hashigh sensitivity and is excellent in printing durability.

<Negative-Working Photosensitive Lithographic Printing Plate>

The negative-working photosensitive lithographic printing plate of thepresent invention is generally composed of a support and aphotosensitive layer made of the above negative-working photosensitivecomposition formed on the support.

Examples of the support include metal plates made of aluminum, zinc,copper, stainless steel, and iron; plastic films made of polyethyleneterephthalate, polycarbonate, polyvinyl acetal, and polyethylene; papersmelt-coated or coated with a synthetic resin, and composite materialsobtained by forming a metal layer on a plastic film by techniques suchas vacuum deposition or laminating; and materials used as the support ofthe lithographic printing plate. Among these supports, aluminum and acomposite support coated with aluminum are preferably used.

The surface of the aluminum support is preferably surface-treated forthe purpose of improving adhesion with the photosensitive layer byenhancing the water retentivity. Examples of the surface treatmentinclude roughening methods such as a brush polishing method, a ballpolishing method, an electrolytic etching method, a chemical etchingmethod, a liquid honing polishing method, a sand blasting method, andcombinations thereof. Among these methods, a roughening treatmentincluding the use of electrolytic etching is preferred.

The electrolytic bath used in electrolytic etching contains an aqueoussolution containing an acid, an alkali or a salt thereof, or an aqueoussolution containing an organic solvent. Among these solutions, anelectrolytic solution containing hydrochloric acid, nitric acid, or asalt thereof is particularly preferred.

The roughened aluminum support is optionally subjected to a desmuttingtreatment using an aqueous solution of an acid or alkali. The aluminumsupport thus obtained is preferably anodized. In particular, ananodizing treatment in a bath containing sulfuric acid or phosphoricacid is preferable.

If necessary, the aluminum support can be treated with a silicate(sodium silicate, potassium silicate), treated with a potassiumzirconate fluoride, treated with phosphomolybdate, treated withpolyacrylic acid, treated with polyvinylsulfonic acid, treated withphosphonic acid, treated with phytic acid, treated with a salt of ahydrophilic organic polymer compound and a divalent metal, treated byundercoating with a water-soluble polymer having a sulfonic acid group,treated with an acidic dye, or treated by electrodeposition withsilicate.

Also an aluminum support obtained by subjecting to a sealing treatmentafter a roughening treatment (graining treatment) and an anodizingtreatment is preferable. The sealing treatment is preferably conductedby dipping the aluminum support in hot water or a hot aqueous solutioncontaining an inorganic or organic salt, or using a steam bath.

The negative-working photosensitive lithographic printing plate of thepresent invention is produced by applying a solution, which is preparedby dissolving or dispersing the negative-working photosensitivecomposition in an organic solvent, on the surface of the support, anddrying the coating film to form a photosensitive layer.

As the organic solvent into which the negative-working photosensitivecomposition is dissolved or dispersed, conventional organic solventsknown in the art can be used. Among these organic solvents, those havinga boiling point within a range from 40 to 200° C., and particularly from60 to 160° C., are selected in view of convenience during drying.

Examples of the organic solvent include alcohols such as methyl alcohol,ethyl alcohol, n- or iso-propyl alcohol, n- or iso-butyl alcohol, anddiacetone alcohol; ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, methyl butyl ketone, methyl amyl ketone, methyl hexylketone, diethyl ketone, diisobutyl ketone, cyclohexanone,methylcyclohexanone, and acetylacetone; hydrocarbons such as hexane,cyclohexane, heptane, octane, nonane, decane, benzene, toluene, xylene,and methoxybenzene; acetates such as ethylacetate, n- oriso-propylacetate, n- or iso-butylacetate, ethylbutylacetate, andhexylacetate; halides such as methylene dichloride, ethylene dichloride,and monochlorobenzene; ethers such as iso-propyl ether, n-butyl ether,dioxane, dimethyl dioxane, and tetrahydrofuran; polyhydric alcohols andderivatives thereof, such as ethylene glycol, ethylene glycol monomethylether, ethylene glycol monomethyl ether acetate, ethylene glycolmonoethyl ether, ethylene glycol monoethyl ether acetate, ethyleneglycol monobutyl ether, ethylene glycol monobutyl ether acetate,ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethyleneglycol dibutyl ether, methoxymethoxy ethanol, diethylene glycolmonomethyl ether, diethylene glycol dimethyl ether, diethylene glycolmethyl ethyl ether, diethylene glycol diethyl ether, propylene glycol,propylene glycol monomethyl ether, propylene glycol monomethyl etheracetate, propylene glycol monoethyl ether, propylene glycol monoethylether acetate, propylene glycol monobutyl ether,3-methyl-3-methoxybutanol, and 1-methoxy-2-propanol; and specialsolvents such as dimethyl sulfoxide, N,N-dimethylformamide, methyllactate, and ethyl lactate. These organic solvents can be used alone orin combination. The solid content in the negative-working photosensitivecomposition to be applied is preferably controlled within a range from 2to 50% by weight. The solid content as used herein refers to componentsexcept for the organic solvent.

As the coating method of the negative-working photosensitivecomposition, for example, roll coating, dip coating, air knife coating,gravure coating, gravure offset coating, hopper coating, blade coating,wire doctor coating, and spray coating methods are used. The coatingweight of the negative-working photosensitive composition is preferablywithin a range from 10 to 100 ml/m².

The negative-working photosensitive composition applied on the supportis usually dried with heated air. The drying temperature (temperature ofheated air) is preferably within a range from 30 to 200° C., andparticularly preferably from 40 to 140° C. A method of raising thetemperature stepwise can also be carried out, in addition to a method ofmaintaining a constant temperature during drying.

Preferred results can sometimes be obtained by removing moisture in thedrying air. The dried air is preferably fed to the coated surface at arate within a range from 0.1 to 30 m/s, and particularly preferably from0.5 to 20 m/s.

The coating weight of the negative-working photosensitive composition iswithin a range from about 0.5 to 5 g/m² in terms of dry weight.

As the negative-working photosensitive lithographic printing plate ofthe present invention is usually subjected to laser irradiation in air,a protective layer can also be formed on the photosensitive layer. Theprotective layer prevents penetration of low molecular compounds such asoxygen and basic substances existing in the air, which inhibit thepolymerization reaction in the photosensitive layer, into thephotosensitive layer, thus making it possible to perform laserirradiation in air. Therefore, performances required to the protectivelayer include low permeability of low molecular compounds such asoxygen, excellent transmitting properties of light used in exposure,excellent adhesion with the photosensitive layer, and easy removal bythe development after laser irradiation.

As the material of the protective layer, for example, a water-solublepolymer compound having comparatively excellent crystallinity can beused. Specific examples thereof include water-soluble polymers such aspolyvinyl alcohol, polyvinyl pyrrolidone, acidic celluloses, gelatin,gum arabic, and polyacrylic acid. The use of polyvinyl alcohol as a maincomponent gives most preferable results in view of basic characteristicssuch as oxygen barrier properties and development-eliminatingproperties. The polyvinyl alcohol used for the protective layer may bepartially substituted with ester, ether and acetal as far as it containsan unsubstituted vinyl alcohol unit for required oxygen barrierproperties and water solubility. Similarly, it may partially contain theother copolymer component.

Examples of the polyvinyl alcohol (PVA) include those which are 71 to100% hydrolyzed and have a molecular weight within a range from 300 to2400. Specific examples thereof include PVA-105, PVA-110, PVA-117,PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HC, PVA-203,PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224, PVA-217EE,PVA-217E, PVA-220E, PVA-224E, PVA-405, PVA-420, PVA-613, and L-8, whichare manufactured by Kuraray Co., Ltd.

The component (selection of PVA, use of additive) and the coating weightof the protective layer are selected taking account of fog, adhesion andscratch resistance, in addition to oxygen barrier properties anddevelopment-eliminating properties. As the hydrolysis rate of PVA to beused (the higher the content of the unsubstituted vinyl alcohol unit inthe protective layer) and film thickness becomes higher, oxygen barrierproperties are improved and it is advantageous in view of sensitivity.However, when oxygen barrier properties are remarkably improved, anunnecessary polymerization reaction may arise during the manufacturingand storage and there may arise problems such as unnecessary fog andimage line thickening during laser irradiation. Also adhesion in theimage area and scratch resistance are very important in view of handlingof the plate. When a hydrophilic layer made of a water-soluble polymeris laminated on a hydrophilic polymerized layer, film release due to lowadhesion is likely to arise and the released portion causes defects suchas poor film curing due to polymerization inhibition of oxygen. Themethod of improving adhesion between two layers includes a method ofmixing 20 to 60% by weight of an acrylic emulsion or a water-insolublevinyl pyrrolidone-vinyl acetate copolymer with a hydrophilic polymercomposed mainly of polyvinyl alcohol.

The negative-working photosensitive lithographic printing plate of thepresent invention can be used as a so-called computer-to-plate (CTP)plate capable of directly writing images on a plate, based on digitalimage information from a computer, using a laser.

In the present invention, as the negative-working photosensitivelithographic printing plate can be handled in daylight, a high-outputlaser having a maximum intensity within a near infrared or infraredrange is used most preferably. Examples of the high-output laser havinga maximum intensity within a near infrared or infrared range includevarious lasers having a maximum intensity within a near infrared orinfrared range from 760 nm to 1200 nm, for example, a semiconductorlaser and YAG laser.

The negative-working photosensitive lithographic printing plate of thepresent invention is written with images in the photosensitive layerusing laser light and the images are developed to remove the non-imagearea using a wet developing method. A lithographic printing platewherein an image area is formed is then obtained. In the presentinvention, the development may be conducted immediately after laserirradiation, but a heat treatment step can also provided between thelaser irradiation step and the development step. The heat treatment ispreferably conducted at a temperature within a range from 80 to 150° C.for 10 seconds to 5 minutes. This heat treatment can decrease laserenergy required to write images during laser irradiation.

An example of the developing solution used in the developing treatmentincludes an aqueous alkali solution (basic aqueous solution).

Examples of the alkali agent used in the developing solution includeinorganic alkali compounds such as sodium silicate, potassium silicate,potassium hydroxide, sodium hydroxide, lithium hydroxide, a sodium,potassium or ammonium salt of secondary or tertiary phosphoric acid,sodium metasilicate, sodium carbonate, and ammonia; and organic alkalicompounds such as monomethylamine, dimethylamine, trimethylamine,monoethylamine, diethylamine, triethylamine, monoisopropylamine,diisopropylamine, n-butylamine, di-n-butylamine, monoethanolamine,diethanolamine, triethanolamine, ethyleneimine, and ethylenediamine.

The content of the alkali agent in the developing solution is preferablywithin a range from 0.005 to 10% by weight, and particularly preferablyfrom 0.05 to 5% by weight. When the content of the alkali agent in thedeveloping solution is less than 0.005% by weight, poor developmenttends to result. On the other hand, when the content is more than 10% byweight, an adverse influence such as erosion of the image area duringthe development is likely to be exerted. Therefore, it is not preferred.

The organic solvent can also be added to the developing solution.Examples of the organic solvent include ethyl acetate, butyl acetate,amyl acetate, benzyl acetate, ethylene glycol monobutylacetate, butyllactate, butyl levulinate, methyl ethyl ketone, ethyl butyl ketone,methyl isobutyl ketone, cyclohexanone, ethylene glycol monobutyl ether,ethylene glycol monobenzyl ether, ethylene glycol monophenyl ether,benzyl alcohol, methylphenyl carbitol, n-amyl alcohol, methylamylalcohol, xylene, methylene dichloride, ethylene dichloride, andmonochlorobenzene.

The amount of the organic acid to be added to the developing solution ispreferably 20% by weight or less, and particularly preferably 10% byweight or less.

If necessary, the developing solution can contain water-solublesulphites such as such as lithium sulfite, sodium sulfite, potassiumsulfite, and magnesium sulfite; hydroxy-aromatic compounds such as analkali-soluble pyrazolone compound, alkali-soluble thiol compound, andmethyl resorcin; hard water softening agents such as polyphosphate andaminopolycarboxylate; and various surfactants, for example, anionicsurfactants such as sodium isopropylnaphthalenesulfonate, sodiumn-butylnaphthalenesulfonate, sodium N-methyl-N-pentadecylaminoacetate,and sodium lauryl sulfate, cationic surfactants, amphoteric surfactants,and fluorine surfactant; and various defoamers.

As the developing solution, a commercially available developing solutionfor a negative or positive presensitized (PS) plate can be used inpractice. Specifically, a solution prepared by diluting a commerciallyavailable concentrated developing solution for a negative or positive PSplate by 1 to 1000 times can be used as the developing solution in thepresent invention.

The temperature of the developing solution is preferably within a rangefrom 15 to 40° C. and the dipping time is preferably within a range fromone second to 2 minutes. If necessary, the surface can also be slightlyrubbed during the development.

The developed lithographic printing plate is washed with water and/ortreated with a water-based desensitizing agent (finishing gum). Examplesof the water-based desensitizing agent include an aqueous solution ofwater-soluble natural polymers such as gum arabic, dextrin, andcarboxymethylcellulose; and water-soluble synthetic polymers such aspolyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid. Ifnecessary, an acid or a surfactant is added to these water-baseddesensitizing agents. After treating with the desensitizing agent, thelithographic printing plate is dried and then used in printing as amachine plate.

For the purpose of improving printing durability of the resultinglithographic printing plate, the lithographic printing plate can also besubjected to a burning treatment or a post exposure treatment after thedevelopment treatment.

The burning treatment can be performed by the steps of (i) first,washing the lithographic printing plate obtained by the treatment methoddescried above to remove the rinsing solution or the gum solution,followed by squeegeing; (ii) subsequently extending a counter-etchingsolution in a uniform manner on the entire plate, followed by drying;(iii) burning the plate for 1 minute to 30 minutes in an oven at atemperature within a range from 180 to 300° C., and (iv) removing thecounter-etching solution by washing the plate with water after the plateis cooled, followed by gum coating and further drying.

The post exposure treatment is performed by subjecting the surface ofthe image area side of the lithographic printing plate to whole surfaceexposure after the development treatment. The post exposure treatment ispreferably subjected to whole surface exposure at exposure energy whichis 50 times or less, more preferably 1 to 30 times, and still morepreferably 2 to 15 times, higher than that in case of laser irradiation.When the exposure energy upon post exposure is more than 50 times higherthan that in case of laser irradiation, sufficient printing durabilitymay not be obtained.

The exposure energy upon post exposure is not specifically limited asfar as it satisfies the above-described relation with the exposureenergy in case of laser irradiation, but is preferably within a rangefrom 10 mJ/cm² to 10 J/cm², and more preferably from 50 mJ/cm² to 8Jcm², in view of treatment time.

Examples of light source used for post exposure include, but are notlimited to, a carbon arc lamp, a high-pressure mercury lamp, anultrahigh-pressure mercury lamp, a low-pressure mercury lamp, a deep UVlamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, a tungstenlamp, a halogen lamp, and an excimer laser lamp. Among these lamps, amercury lamp and a metal halide lamp are preferable, and a mercury lampis particularly preferable.

The post exposure treatment may be performed while the lithographicprinting plate is allowed to stand or is continuously transferred. Inview of strength of the image area, light intensity on the surface ofthe lithographic printing plate is preferably controlled within a rangefrom 20 mW/cm² to 1 W/cm², and more preferably from 30 mW/cm² to 500mW/cm. The light intensity on the surface of the lithographic printingplate can be controlled within the range described above using a methodof exposing light, comprising increasing an output (W) of a light sourceby increasing an output of a light source to be used, or increasing anoutput of a light source by increasing an output per unit length in caseof a bar-shaped light source, or a method of exposing to light byenabling the surface of the lithographic printing plate to come closerto a light source.

Upon post exposure, the surface temperature of the lithographic printingplate is preferably controlled within a range from 40 to 300° C., andmore preferably from 50 to 200° C., by radiant heat from a post exposurelight source, or heating using a hot plate, dryer or ceramic heater.Radiant heat from a light source is preferably employed as heating meansbecause it is simple and easy.

The negative-working photosensitive lithographic printing platedescribed above is less likely to suffer polymerization inhibition byoxygen during radical polymerization, and also has high sensitivity andis excellent in printing durability because a negative-workingphotosensitive composition having high adhesion is used as aphotosensitive layer.

The negative-working photosensitive composition of the present inventioncan be used for various purposes, such as a photoresist and a colorfilter, in addition to the use as a lithographic printing plate.

EXAMPLES

The present invention will be described in more detail by way ofexamples, but the present invention is not limited to these examples.

(Synthesis of Acrylic Resin (E-1))

In a 500 ml three-necked flask equipped with a capacitor and a stirrer,200.00 g of methyl ethyl ketone was charged and, after replacing theatmosphere in the flask by nitrogen, the liquid was heated to 65° C.Then, a solution prepared by dissolving 18.00 g (0.142 mols) of allylmethacrylate, 9.00 g (0.169 mols) of acrylonitrile, 3.00 g (0.034 mols)of methacrylic acid and 0.40 g of 2,2′-azobis(2,4-dimethylvaleronitrile)in 70.00 g of methyl ethyl ketone was added dropwise over 2 hours. Onehour after the completion of the dropwise addition, 0.20 g of2,2′-azobis(2,4-dimethylvaleronitrile) was added, followed by heatingfor 4 hours. The reaction solution was poured into 2 liters of waterwhile stirring to precipitate a white polymer. The resulting polymer waswashed with water and then vacuum-dried to obtain an acrylic resin(E-1). The amount of the resulting polymer was 28.50 g and the yield was95% by weight.

(Synthesis of Acrylic Resin (E-2))

In a 500 ml three-necked flask equipped with a capacitor and a stirrer,150.00 g of ethylene glycol monomethyl ether was charged and, afterreplacing the atmosphere in the flask by nitrogen, the liquid was heatedto 80° C. Then, a solution prepared by dissolving 40.00 g (0.307 mols)of hydroxyethyl methacrylate, 30.00 g (0.565 mols) of acrylonitrile,10.00 g (0.099 mols) of methyl methacrylate, 10.00 g (0.116 mols) ofmethacrylic acid and 0.40 g of 2,2′-azobisisobutyronitrile in 60.00 g ofethylene glycol monomethyl ether was added dropwise over 2 hours. Onehour after the completion of the dropwise addition, 0.20 g of2,2′-azobisisobutyronitrile was added, followed by heating for 8 hours.The reaction solution was poured into 2 liters of water while stirringto precipitate an yellowish white polymer. The resulting polymer waswashed with water and then vacuum-dried to obtain an acrylic resin(E-2). The amount of the resulting polymer was 85.50 g and the yield was95% by weight.

Example 1

As shown in the formulation in Table 1, 0.2 g (2% by weight) of a nearinfrared absorbable cationic dye (A-1) represented by the followingformula (A-1) as the infrared absorber (A), 0.6 g (6% by weight) of anorganoboron compound (B-1) represented by the following formula (B-1) asthe organoboron compound (B), 3.0 g (30% by weight) of a polyfunctionalurethane acrylate (manufactured by Bomar Co., UR-3447) as the compoundhaving a polymerizable unsaturated group (C), 0.9 g (9% by weight) of a2-hydroxy-4-methoxybenzophenone-5-sulfonate of a condensate ofparadiazodiphenylamine and formaldehyde as the diazo resin (D), 4.8 g(48% by weight) of an acrylic resin (E-1), which is an alkali-solubleresin, as the binder resin (E), 0.2 g of DC-190 (10%, ethylene glycolmonomethyl ether solution, manufactured by Eastman Kodak Company) as thesurfactant, and 0.3 g of Crystal Violet as the colorant were dissolvedin a solvent mixture of 70.0 g of ethylene glycol monomethyl ether and20.0 g of methyl ethyl ketone to prepare a coating solution of anegative-working photosensitive composition.

An aluminum plate having a thickness of 0.30 mm was degreased with anaqueous sodium hydroxide and then electrolytically grained in a 2%hydrochloric acid bath to obtain a grained plate having a center lineaverage roughness (Ra) of 0.55 μm. The resulting grained plate wasanodized in a 20% sulfuric acid bath at a current density of 2 A/dm² toform an oxide film of 2.6 g/m², was passed through an aqueous 2.5%sodium silicate at 70° C. for 30 seconds, was washed with water and wasthen dried to obtain an aluminum support. On the aluminum support, thecoating solution of the negative-working photosensitive composition wasapplied using a roll coater and dried at 100° C. for 40 seconds toobtain a negative-working photosensitive lithographic printing plate.The weight of the dry coating was 1.5 g/m².

Using this photosensitive lithographic printing plate immediately afterthe production, imagewise exposure was conducted by an exposing machine(Trendsetter 3244, manufactured by CREO Corp., wavelength: 830 nm, laserpower: 10 W, rotational speed: 185 rpm) equipped with a near infraredsemiconductor laser. Using an automatic processor (manufactured by FUJIPHOTO FILM CO., LTD., PS-900N) and a developing solution (manufacturedby FUJI PHOTO FILM CO., LTD., a mixture of 80 parts by weight of adeveloping solution DN-6, 120 parts by weight of water and 200 parts byweight of a surfactant PELEX NBL manufactured by Kao Corporation.), theexposed photosensitive lithographic printing plate was subjected to adeveloping treatment at 30° C. for 20 seconds. Sensitivity and printingdurability of the resulting lithographic printing plate were evaluated.The results are shown in Table 2.

(Sensitivity)

With respect to the dot size of the lithographic printing plate afterbeing subjected to the development treatment, reproducibility wasconfirmed and evaluated, In Table 2, with respect to the evaluationcriteria, “A” is excellent in dot reproducibility, and the ratingbecomes poor in the sequence of “B”, “C”, and “D”, and “E” is the mostpoor.

(Printing Durability)

The lithographic printing plate used in the evaluation of sensitivitywas affixed to a printing press (Sprint-26 (manufactured by KomoriCorporation) and subsequently printing was performed using GEOS-G(manufactured by DAINIPPON INK & CHEMICALS Co., Ltd.) as the ink andNA108-W (manufactured by DAINIPPON INK & CHEMICALS Co., Ltd.) as thefountain solution. The printing test was performed by stopping theprinting press every 30,000 impressions and the image area was observed.Printing durability was evaluated from the degree of ablation. In Table2, with respect to the evaluation criteria, “A” is excellent in printingdurability, and the rating becomes poor in the sequence of “B”, “C”, and“D”, and “E” is the most poor.

Examples 2 and 3, Comparative Examples 1 to 4

In the same manner as in Example 1, except that the formulation of thecoating solution was changed as shown in Table 1, negative-workingphotosensitive lithographic printing plates were produced and evaluated.The results are shown in Table 2. The organoboron compound (B-2) in theTable 1 has a structure represented by the following formula (B-2), andthe near infrared absorbable cationic dye (A-2) has a structurerepresented by the following formula (A-2). TABLE 1 Coating solution ofnegative-working photosensitive composition Unit: g Examples ComparativeExamples 1 2 3 1 2 3 4 Near infrared absorbable cationic dye (A-1) 0.20.2 0.2 0.2 0.2 0.2 Near infrared absorbable cationic dye (A-2) 0.2Organoboron compound (B-1) 0.6 0.6 0.6 0.6 0.6 Organoboron compound(B-2) 0.6 Polyfunctional urethane acrylate 3.0 3.0 3.0 3.0 3.0 3.02-hydroxy-4-methoxybenzophenone-5-sulfonate of 0.9 0.9 0.9 0.9condensate of paradiazodiphenylamine with formaldehydep-toluenesulfonate of condensate of 0.9 paradiazodiphenylamine withformaldehyde 2-hydroxy-4-methoxybenzophenone-5-sulfonate of 0.9paradiazodiphenylamine Acrylic resin (E-1) 4.8 4.8 4.8 4.8 4.8 4.8Acrylic resin (E-2) 4.8 DC190 (10% solution) 0.2 0.2 0.2 0.2 0.2 0.2 0.2Crystal Violet 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Ethylene glycol monomethylether 70.0 70.0 70.0 70.0 70.0 70.0 70.0 Methyl ethyl ketone 20.0 20.020.0 20.0 20.0 20.0 20.0

TABLE 2

(A-1)

(B-1)

(A-2)

(B-2) Examples Comparative Examples Evaluation 1 2 3 1 2 3 4 SensitivityA B A E E E E Printing durability A B A E E E E

As is apparent from the results shown in Table 2, the negative-workingphotosensitive lithographic printing plates of Examples 1 to 3 exhibitedhigh sensitivity and were excellent in printing durability. On the otherhand, the negative-working photosensitive lithographic printing platesof Comparative Examples 1 and 2 wherein the photosensitive layercontains no diazo resin (D), the negative-working photosensitivelithographic printing plate of Comparative Example 3 wherein thephotosensitive layer contains no organoboron compound (B) and thenegative-working photosensitive lithographic printing plate ofComparative Example 4 wherein the photosensitive layer contains nocompound having a polymerizable unsaturated group (C) exhibited lowsensitivity and were inferior in printing durability.

(Synthesis of Polyurethane Resin)

In a 500 ml three-necked flask equipped with a capacitor and a stirrer,after replacing the atmosphere in the flask with nitrogen, 21.50 g (0.1mols) of 2,2-bis(hydroxymethyl)propionic acid, 5.30 g (0.05 mols) ofdiethylene glycol and 6.60 g (0.05 mols) of glycerol monoallyl etherwere added and then dissolved in 125.25 g of 1,4-dioxane. 0.30 g ofdi-n-butyltin dilaurate as the catalyst was added and then 50.10 g (0.2mols) of 4,4-diphenylmethane diisocyanate was added, followed by heatingat 100° C. for 5 hours. The reaction was completed after confirming byIR measurement that remaining isocyanate groups disappeared. Thereaction solution was poured into 2 liters of water to precipitate awhite polymer. The polymer was washed with water and then vacuum-driedto obtain a polyurethane resin having a carboxyl group and an allylgroup. The amount of the resulting polymer was 75.00 g and the yield was90% by weight.

Example 4

As shown in the formulation in Table 3, 0.2 g (2% by weight) of a nearinfrared absorbable cationic dye (A-1) represented by the followingformula (A-1) as the infrared absorber (A), 0.6 g (6% by weight) of anorganoboron compound (B-1) represented by the following formula (B-1) asthe organoboron compound (B), 3.0 g (30% by weight) of a polyfunctionalurethane acrylate. (manufactured by Bomar Co., UR-3447) as the compoundhaving a polymerizable unsaturated group (C), 0.9 g (9% by weight) of a2-hydroxy-4-methoxybenzophenone-5-sulfonate of a condensate ofparadiazodiphenylamine and formaldehyde as the diazo resin (D), 4.8 g(48% by weight) of the above polyurethane resin, which is analkali-soluble resin, as the binder resin (E), 0.2 g of DC-190 (10%,ethylene glycol monomethyl ether solution, manufactured by Eastman KodakCompany) as the surfactant, and 0.3 g of Crystal Violet as the colorantwere dissolved in a solvent mixture of 70.0 g of ethylene glycolmonomethyl ether and 20.0 g of methyl ethyl ketone to prepare a coatingsolution of a negative-working photosensitive composition.

An aluminum plate having a thickness of 0.30 mm was degreased with anaqueous sodium hydroxide and then electrolytically polished in a 2%hydrochloric acid bath to obtain a grained plate having a center lineaverage roughness (Ra) of 0.6 μm. The resulting grained plate wasanodized in a 20% sulfuric acid bath at a current density of 2 A/dm² toform an oxide film of 2.7 g/m², which was passed through an aqueous 2.5%sodium silicate at 70° C. for 30 seconds, washed with water and thendried to obtain an aluminum support. On the aluminum support, thecoating solution of the negative-working photosensitive composition wasapplied using a roll coater and dried at 100° C. for one minute toobtain a negative-working photosensitive lithographic printing plate.The weight of the dry coating film was 1.5 g/m².

Using this photosensitive lithographic printing plate immediately afterthe production, imagewise exposure was conducted by an exposing machine(Trendsetter 3244, manufactured by CREO Corp., wavelength: 830 nm, laserpower: 9 W, rotational speed: 150 rpm) equipped with a near infraredsemiconductor laser. Using an automatic processor (manufactured by FUJIPHOTO FILM CO., LTD., PS-900N) and a developing solution (manufacture byFUJI PHOTO FILM CO., LTD., a solution mixture of 80 parts by weight of adeveloping solution DN-6, 120 parts by weight of water and 200 parts byweight of a surfactant PELEX NBL manufactured by Kao Corporation.), theexposed photosensitive lithographic printing plate was subjected to adeveloping treatment at 30° C. for 25 seconds. Sensitivity and printingdurability of the resulting lithographic printing plate were evaluated.The results are shown in Table 4.

(Sensitivity)

With respect to the dot size of the lithographic printing plate afterbeing subjected to the development treatment, reproducibility wasconfirmed and evaluated, In Table 2, with respect to the evaluationcriteria, “A” is excellent in dot reproducibility, and the ratingbecomes poor in the sequence of “B”, “C”, and “D”, and “E” is the mostpoor.

(Printing Durability)

The lithographic printing plate used in the evaluation of sensitivitywas affixed to a printing press (Sprint-26 (manufactured by KomoriCorporation) and subsequently printing was performed using EOS-G(manufactured by DAINIPPON INK & CHEMICALS Co., Ltd.) as the ink andNA108-W (manufactured by DAINIPPON INK & CHEMICALS Co., Ltd.) as thefountain solution. The printing test was performed by stopping theprinting press every 30,000 impressions and the image area was observed.Printing durability was evaluated from the degree of ablation. In Table2, with respect to the evaluation criteria, “A” is excellent in printingdurability, and the rating becomes poor in the sequence of “B”, “C”, and“D”, and “E” is the most poor.

Examples 5 and 6

In the same manner as in Example 4, except that the formulation of thecoating solution was changed as shown in Table 3, negative-workingphotosensitive lithographic printing plates were produced and evaluated.The evaluation results are shown in Table 4. The organoboron compound(B-2) in the Table 4 has a structure represented by the formula (B-2),and the near infrared absorbable cationic dye (A-2) has a structurerepresented by the formula (A-2). TABLE 3 Coating solution ofnegative-working photosensitive composition unit: g Examples 4 5 6 Nearinfrared absorbable cationic dye 0.2 0.2 (A-1) Near infrared absorbablecationic dye 0.2 (A-2) Organoboron compound (B-1) 0.6 0.6 Organoboroncompound (B-2) 0.6 Polyfunctional urethaneacrylate 3.0 3.0 3.02-hydroxy-4-methoxybenzophenone-5- 0.9 0.9 sulfonate of condensate ofparadiazodiphenylamine with formaldehyde Hexafluorophosphate ofcondensate of 0.9 paradiazodiphenylamine with formaldehyde Polyurethaneresin 4.8 4.8 4.8 DC190 (10% solution) 0.2 0.2 0.2 Crystal Violet 0.30.3 0.3 Ethylene glycol monomethyl ether 70.0 70.0 70.0 Methyl ethylketone 20.0 20.0 20.0

TABLE 4 Examples Evaluation 4 5 6 Sensitivity A B A Printing durabilityA B A

As is apparent from the results shown in Table 4, the negative-workingphotosensitive lithographic printing plates of Examples 4 to 6 exhibitedhigh sensitivity and were excellent in printing durability.

EFFECTS OF THE INVENTION

As described above, as the negative-working photosensitive compositionof the present invention contains an infrared absorber (A), anorganoboron compound (B) which functions as a polymerization initiatorby using in combination with the infrared absorber (A), a compoundhaving a polymerizable unsaturated group (C) and a diazo resin (D), thenegative-working photosensitive composition can be cured by infraredrays and is less likely to suffer polymerization inhibition by oxygenduring radical polymerization, and also exhibits high adhesion withmetal.

As the negative-working photosensitive lithographic printing plate ofthe present invention comprises a support, and a photosensitive layercontaining the negative-working photosensitive composition of thepresent invention formed on the support, the negative-workingphotosensitive lithographic printing plate is capable of directlyforming images by irradiating with infrared rays from a solid or asemiconductor laser based on digital signals, and also has highsensitivity and excellent printing durability.

1. A negative-working photosensitive composition comprising: (A) aninfrared absorber, (B) an organoboron compound which functions as apolymerization initiator by using in combination with the infraredabsorber (A), (C) a compound having a polymerizable unsaturated group,and (D) a diazo resin.
 2. The negative-working photosensitivecomposition according to claim 1, wherein the infrared absorber (A) is anear infrared absorbable cationic dye represented by the followingformula (1):D⁺A⁻  (1) wherein D⁺ represents a cationic dye having an absorptionwithin a near infrared range, and A⁻ represents an anion.
 3. Thenegative-working photosensitive composition according to claim 1,wherein the organoboron compound (B) is an ammonium salt of a quaternaryboron anion represented by the following formula (2):

wherein R¹, R², R³ and R⁴ each independently represents an alkyl group,an aryl group, an alkaryl group, an allyl group, an aralkyl group, analkenyl group, an alkynyl group, an alicyclic group, or a saturated orunsaturated heterocyclic group, and at least one of R¹, R², R³ and R⁴ isan alkyl group having 1 to 8 carbon atoms, and R⁵, R⁶, R⁷ and R⁸ eachindependently represents a hydrogen atom, an alkyl group, an aryl group,an allyl group, an alkaryl group, an aralkyl group, an alkenyl group, analkynyl group, an alicyclic group, or a saturated or unsaturatedheterocyclic group.
 4. The negative-working photosensitive compositionaccording to claim 1, further comprising a binder resin (E).
 5. Thenegative-working photosensitive composition according to claim 4,wherein the binder resin (E) is an alkali-soluble resin.
 6. Thenegative-working photosensitive composition according to claim 1 whereinthe compound having a polymerizable unsaturated group is a monomer oroligomer having at least one addition-polymerizable ethylenicallyunsaturated group, and comprises 5 to 60% weight based on the solidcontent of the composition.
 7. A negative-working photosensitivelithographic printing plate comprising a support and a photosensitivelayer containing the negative-working photosensitive compositionaccording to claim 1 formed on the support.
 8. The printing plate ofclaim 7 wherein the support is an electrolytically etched and anodizedaluminum support.
 9. The printing plate further comprising anoxygen-impermeable protective layer.
 10. A method of imaging comprisingdirect computer to plate imaging of the printing plate of claim 7.